There are many transparency films that are writable in some fashion or another. Writability has been provided for these films by various means including surface treatment and application of materials onto the film substrate. Solvent based pen writability is typically not an insurmountable problem when it is necessary to write on a film. However, films that will work successfully with water based writing instruments typically have a number of deficiencies. Many configurations of films that are writable using both solvent and water-based instruments tend to use polyvinyl pyrollidone or polyvinyl alcohol as a water accepting agent. Varying chemistry is used to immobilize the water-accepting polymer to improve rubbing resistance and avoid tack of the coating. Immobilization is usually accomplished through crosslinking, inter-penetrating polymer networks, or ionic interactions.
Many constructions accept water based and solvent based inks, dry in a short time, and are resistant to pressure from moist fingers. Typically, these materials are transparent for use on an overhead projector. However, in general, these films are smooth and therefore do not accept pencil writing. Pencil writing is typically not a requirement of an overhead transparency.
Several examples of writable films have been described. These include for example, U.S. Pat. No. 5,126,194 wherein an ink jet transparency is described as having polyvinyl pyrollidone, a sulfonated polyester, a polyalkylene oxide, polyvinyl alcohol, nonylphenoxypolyglycidol, and inert particles coated onto a polyester film substrate. This construction performs well at room temperature, but the coating is not robust and durable under heat and humidity aging, and turns into a viscous liquid during heat and humidity aging.
Many coating formulations containing water-soluble polymers such as polyvinyl pyrollidone, sulfonated polyesters, or polyvinyl alcohol tend to exhibit similar problems with heat and humidity aging.
An alternative to examples of writable films as described above is examples of synthetic papers or tracing films. These papers tend to be roughened polymeric films. In JP 256607, polyester film was coated with a graft copolymer resin that is composed of an acrylic polymer as a principle chain, and a hydroxyl containing acrylic polymer as a branch chain. Acrylic polymers for the principle chain include polymers of acrylic acid, methacrylic acid, and their metal or ammonium salts. The film claims to have a good writing property, solvent resistance, adhesion of the coating layer, and surface roughness. Another example is JP 97,528/82 in which a polyester film was coated with a water-soluble cationic acrylic resin and benzophenone, which was subsequently UV cured for water resistance. Another example is JP 97,684/79, which describes a mixture of polyvinyl alcohol, a synthetic copolymer, and clay coated on PVDC (polyvinylidene chloride) primed polyester and used as a writable film.
For example, water-absorbing materials that are solvent insoluble have been described. U.S. Pat. No. 4,887,097 describes an ink jet recording medium, which contains particles of solvent insoluble resin that is capable of absorbing water in an amount of 50 times or more as much as its own weight. Examples of solvent insoluble resin particles include natural resins such as albumin, gelatin, casein, starch, cationic starch, gum arabic, and potassium alginate and synthetic resins such as polyvinyl alcohol, polyamide, polyacrylamide, quarternary polyvinyl pyrollidone, polyethyleneimine, polyvinylpyridinium halide, melamine resins, polyurethane, polyester, and sodium polyacrylate.
In WO 96/23659, a coating composition for a plastic film is described. The coating composition is made from an acrylic polymer or ionomer resin and an ink receptive particulate, such as a molecular sieve and/or a carbohydrate polymer such as cellulose, carboxymethyl cellulose, or cornstarch. The coating composition facilitates adhesion of ink to the polyolefin film and reduces the dry time of the ink to less than two minutes. The acrylic polymer contains carboxylic acid selected from the group consisting of acrylic acid, methacrylic acid, and mixtures thereof.
Some examples of writable adhesive coated products have been described. For example, U.S. Pat. No. 4,708,907 describes a writable adhesive tape consisting of a polyolefin substrate, having on one side an adhesive layer and on the opposite side a writable anti-adhesive layer. The writable anti-adhesive layer comprises 25% to 55% by weight of a chlorinated polyolefin, 20% to 50% by weight of a polyaldehyde resin together with 5% to 20% by weight of an anti-adhesive agent, and 25% by weight of a matting charge.
Another example (U.S. Pat. No. 4,985,302) describes a removable self-adhesive sheet with a writable surface. In this example, the sheet material is a polymer film selected from the group consisting of polyvinyl chloride, polypropylene, cellulose acetate, polyester, cellophane, high density polyethylene, or polyolefin coextrusion. The writable side of the sheet is coated with a mixture of a pigment, vinyl or acrylic resin, synthetic wax, epoxide stabilizer, phthallic acid esters, and the solvents ethyl acetate and ethanol.